Exercise 3.32: The procedures to be run during
each time segment of the agenda are kept in a queue.  Thus, the procedures for
each segment are called in the order in which they were added to the agenda
(first in, first out).  Explain why this order must be used.  In particular,
trace the behavior of an and-gate whose inputs change from 0, 1 to 1, 0 in the
same segment and say how the behavior would differ if we stored a segment’s
procedures in an ordinary list, adding and removing procedures only at the
front (last in, first out).